I'm discovering that WORM is a world in itself.
After taking forever to try to image a 470MB disc and taking forever to
do it because of automatic retries on unwritten sectors, I've discovered
that WORM has a SCSI2 command that's unique to it--38H, "Medium Scan"
which can be used to identify groups of written or blank blocks. There
are, of course, other optional WORM-specific commands, but I thought
that I'd pass this one along, as it doesn't occur in any other medium
type, as far as I'm aware.
--Chuck